The present invention generally pertains to a method of operating microsurgical instruments. More particularly, but not by way of limitation, the present invention pertains to a method of operating microsurgical instruments used in posterior segment ophthalmic surgery, such as vitrectomy probes.
Many microsurgical procedures require precision cutting and/or removal of various body tissues. For example, certain ophthalmic surgical procedures require the cutting and/or removal of the vitreous humor, a transparent jelly-like material that fills the posterior segment of the eye. The vitreous humor, or vitreous, is composed of numerous microscopic fibers that are often attached to the retina. Therefore, cutting and removal of the vitreous must be done with great care to avoid traction on the retina, the separation of the retina from the choroid, a retinal tear, or, in the worst case, cutting and removal of the retina itself.
The use of microsurgical cutting probes in posterior segment ophthalmic surgery is well known. Such vitrectomy probes are typically inserted via an incision in the sclera near the pars plana. The surgeon may also insert other microsurgical instruments such as a fiber optic illuminator, an infusion cannula, or an aspiration probe during the posterior segment surgery. The surgeon performs the procedure while viewing the eye under a microscope.
Conventional vitrectomy probes typically include a hollow outer cutting member, a hollow inner cutting member arranged coaxially with and movably disposed within the hollow outer cutting member, and a port extending radially through the outer cutting member near the distal end thereof. Vitreous humor is aspirated into the open port, and the inner member is actuated, closing the port. Upon the closing of the port, cutting surfaces on both the inner and outer cutting members cooperate to cut the vitreous, and the cut vitreous is then aspirated away through the inner cutting member. U.S. Pat. Nos. 4,577,629 (Martinez); 5,019,035 (Missirlian et al.); 4,909,249 (Akkas et al.); 5,176,628 (Charles et al.); 5,047,008 (de Juan et al.); 4,696,298 (Higgins et al.); and 5,733,297 (Wang) all disclose various types of vitrectomy probes, and each of these patents is incorporated herein in its entirety by reference.
Conventional vitrectomy probes include xe2x80x9cguillotine stylexe2x80x9d probes and rotational probes. A guillotine style probe has an inner cutting member that reciprocates along its longitudinal axis. A rotational probe has an inner cutting member that reciprocates around its longitudinal axis. In both types of probes, the inner cutting members are actuated using various methods. For example, the inner cutting member can be moved from the open port position to the closed port position by pneumatic pressure against a piston or diaphragm assembly that overcomes a mechanical spring. Upon removal of the pneumatic pressure, the spring returns the inner cutting member from the closed port position to the open port position. As another example, the inner cutting member can be moved from the open port position to the closed port position using a first source of pneumatic pressure, and then can be moved from the closed port position to the open port position using a second source of pneumatic pressure. As a further example, the inner cutting member can be electromechanically actuated between the open and closed port positions using a conventional rotating electric motor or a solenoid. U.S. Pat. No. 4,577,629 provides an example of a guillotine style, pneumatic piston/mechanical spring actuated probe. U.S. Pat. Nos. 4,909,249 and 5,019,035 disclose guillotine style, pneumatic diaphragm/mechanical spring actuated probes. U.S. Pat. No. 5,176,628 shows a rotational dual pneumatic drive probe.
With each of the above-described conventional vitrectomy probes, the inner cutting member is always actuated, and thus the port is opened and closed, at a particular cycle or cut rate. When the port is open, it is most often occluded by pieces of vitreous humor or other tissue that are being aspirated into the open port via vacuum. Such tissue is not cut and aspirated away from the port until the next stroke of the inner cutting member as determined by the given cut rate. Therefore, conventional vitrectomy probes spend more time in an occluded state than actually cutting and aspirating away tissue. In addition, when actuation of the inner cutting member is determined by a given cut rate, there is sometimes no vitreous or other tissue located in the port to cut when the inner member is actuated.
Given the above, a need exists for an improved method of operating a vitrectomy probe or other microsurgical cutting instrument that does not suffer from the above-described limitations. The improved method should be safe for the patient, easy for the surgeon to use, and economically feasible.
One aspect of the present invention comprises a method of operating a microsurgical instrument. The instrument includes a port for receiving tissue and an inner cutting member. A flow of tissue is induced into the port with a vacuum source. The port is at least partially occluded with the tissue. The occlusion is detected, and the inner cutting member is actuated to close the port and cut the tissue.
The microsurgical instrument may comprise a vitrectomy probe or other cutting probe. The occlusion may be detected by detecting a decrease in fluid flow in the inner cutting member, or a portion of the instrument or a surgical system fluidly coupled to the inner cutting member. The occlusion may also be detected by detecting an increase in vacuum in the inner cutting member, or a portion of the instrument or a surgical system fluidly coupled to the inner cutting member.